One type of floppy disk driving device is known, in which a slip pad is adhered to a hub table which in turn is secured to a spindle. The metallic disk hub of a floppy disk is magnetically attracted and held through this slip pad so that the floppy disk is driven to be rotated by rotating the spindle.
FIGS. 6 and 7 show an example of the type described above of floppy disk driving devices. In FIGS. 6 and 7, a hub table 12 is secured to a spindle 11 driven to be rotated by a motor and a slip pad 15 is adhered to the upper surface of the hub table, surrounding the spindle 11. The hub table 12 is made of resin magnet as a whole and magnetized, or a ring-shaped permanent magnet is buried in the hub table 12. In this way, the metallic disk hub of a floppy disk is attracted toward the hub table 12 so as to hold the disk hub through the slip pad 15. A hole 13 is formed in the hub table 12 at a position near the periphery. As well known, a plate spring is mounted on the lower surface of the hub table 12 and a driving pin fixed on this plate spring stands on the upper surface of the hub table 12 through the hole 13 stated above, the plate spring and driving driving pin being not shown in the figure. The upper end portion of the spindle 11 protruding from the upper surface of the hub table 12 is inserted in the central hole of the disk hub. Further, the disk hub is brought into and held in a predetermined position by inserting the driving pin stated above in the window hole of the disk hub so that the driving pin, supported on and biased by the leaf spring, adjusts the position of the disk hub and in this positioning state the disk hub and the floppy disk mounted integrally therewith are driven to be rotated.
As a prior art example using the slip pad in this way, that described in JP-Patent-A-60-147962 and corresponding U.S. Pat. No. 4,654,733 can be cited. In this prior art example a disk hub attracting magnet disposed separately from the hub table is secured to the hub table.
In a floppy disk driving device having a structure in which a slip pad is adhered on the disk hub attracting side of the hub table, the contacting surfaces of the disk hub and the slip pad should both be smooth. If these contacting surfaces are not smooth, the rotational torque therebetween is increased, when the disk hub is set on the slip pad, which gives rise to an inconvenience that the disk hub is not set smoothly on the hub table.
Further, the inventors have found that the conventional floppy disk driving device involves the following problem; namely, that adhesive is pressed out from the outer periphery of the slip pad, and such pressed out adhesive adheres on the disk hub attracting surface of the hub table. This adhesive prevents a smooth contact between the contacting surfaces of the disk hub and the slip pad and increases the rotational torque between the disk hub and the slip pad. The biasing force of the leaf spring is not large enough for the driving pin to adjust the position of the disk, so that the disk hub cannot be set smoothly on the hub table.
There was another problem that, when the slip pad is fabricated by punching, the periphery of the pad has a tendency to be bent in the punching direction so that, when it is adhered on a plane, the resulting surface will not be even so that, when a disk is mounted thereon, it cannot be parallel to the plane.